[FIXED] Django: paginated ListView database performance

Issue

I have a ListView with pagination:

class StoriesListView(ListView):
    model = Story
    paginate_by = 20

    def get_queryset(self):
        return Story.objects.all().order_by('-updated_at')

I have 1000 Story objects in the database. What happens when the user loads my view? Will all the 1000 be queried from the database or only 20? How can I optimize this?

Solution

It depends on how you are using it. QuerySet objects are lazy, and in this particular case, the SQL query will add LIMIT and OFFSET, so the query will always return only 20 results. But when you want to use related objects in your template, you have to optimize your query with select_related or prefetch_related methods ( otherwise you will end up with additional queries for each record from the main query )

I think you should read how to optimize database access in django framework.

Hope this helps.

Answered By - dydek